Most coaxial-type connectors use a circular center contact, a hollow cylindrical outer contact, and a tubular insulation between them. The cylindrical shapes result in relatively expensive manufacturing methods such as machining of the inner contact to form cylindrical shapes. Also, retention features generally must be attached to the outside of the outer contact, since their insertion into slots in the insulation would result in a sudden change in impedance there, resulting in reflectance of signals and consequent increase VSWR (voltage standing wave ratio) and signal losses. Each coaxial type connector has a defined characteristic impedance with 50 ohms being the most common, and with losses increasing with deviations from the defined characteristic impedance at locations in the connector. A coaxial-type contact assembly, or connector, with inner and outer contacts separated by insulation, for carrying signals in the range of megahertz and gigahertz, which could be constructed at low cost and which enabled the provision of cutouts in selected areas of the insulation for retention features without seriously degrading the connector, would be of value.
In accordance with one embodiment of the present invention, a coaxial-type contact assembly, or connector, is provided which is designed for low cost construction and assembly and the inclusion of simple retention features. The connector includes an inner contact extending along the connector axis, an outer contact, and an insulation between them. Along a major region that extends at least one third of the length of the inner contact, the distance between the inner contact and a side surface of the outer contact is at least 140 percent of the distance between the inner contact and upper surface of the outer contact. This results in lowest impedance at primary sectors between the inner contact and the upper and lower surfaces of the outer contact, and much higher impedance at secondary sectors at the opposite sides of the inner contact. As a result, cutouts at opposite sides of the insulation, which lie substantially only in the secondary sectors, do not result in a large change in characteristic impedance that would result in a large increase in losses. The inner contact, like the outer one, can be formed of sheet metal with a constant thickness along most of its length, and with a width that can vary to provide retention features in the inner contact, for low cost construction.
In one connector, the outer contact is of rectangular cross-section with at least a 140% greater width than height. Also, the inner contact lies at the middle of the cross-section so it is equally spaced from the top and bottom of the outer contact. In that case, primary sectors lie above and below the inner contact and secondary sectors lie on opposite sides. The outer contact can have a variety of shapes, so long as there are primary and secondary sectors of distinctly different impedances (e.g. with the distance between contacts at least 40% greater at the secondary sector(s) than at the primary sector(s), with the impedance along the length of the primary sector or sectors being substantially constant.
Termination of the rear termination end of the inner contact to the center conductor of a coaxial cable, can be accomplished while the inner contact lies locked in the rest of the connector, by allowing the outer contact and the insulation to have parts that can be shifted away from positions that closely surround the rear end of the inner contact. After joining as by crimping a tubular portion of the inner contact around the cable center conductor, parts of the insulation and outer contact can be moved to positions closely around the rear end of the inner contact. The insulation can be formed as two identical members with rear ends each forming a joint-surrounding part connected by a band to the rest of the insulation member, with the band molded integrally with the main part and joint-surrounding part of the insulation.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.